A. Field of the Invention
The invention relates to a method of fixing impeller blades to an impeller shell of a torque converter.
B. Description of the Related Art
A torque converter has three kinds of vane wheels, an impeller, a turbine and a stator, all arranged in an annular fluid-filled chamber defined in the torque converter. The vane wheels are adapted to transmit torque from an input rotary member to an output rotary member via working fluid in the annular fluid-filled chamber. The impeller includes an impeller shell, a large number of circumferentially spaced apart impeller blades located inside the impeller shell and an annular impeller core fixed to radially inward sides of the impeller blades.
In a conventional impeller, each impeller blade is fixed to the impeller shell in the following manner. First, the impeller shell is formed with a plurality of concavities or recesses via an embossing or deformation process. Next, the impeller blades are each formed with a plurality of projections. Next, the projections are fitted into -the concavities or recess of the impeller shell. Finally, the impeller blades are fixed to the impeller shell by brazing, or another similar welding process.
When the brazing or other similar welding process is employed for fixing the impeller blades to the impeller shell, the impeller blades and portions of the impeller shell are heated causing the impeller shell to be thermally deformed, often to a large extent.
Another method of fixing impeller blades includes forming concavities in the impeller shell, inserting tabs formed on the impeller blades into the concavities, then caulking a portion near the concavity by punching or otherwise deforming the impeller blade and/or. impeller shell. The second method is less expensive than the first method that employs brazing.
In the conventional fixing method, however, caulking, e.g., punching causes deformation in the impeller shell. This is because the outer surface of the impeller shell is entirely supported on a support base, and a portion of the support base that bears the punching load may vary each time the punching is performed. For example, if the portion bearing the load is spaced apart slightly from the portion of the impeller shell being caulked, or if the portion bearing the load is not uniformly shaped to conform to the shape of the impeller shell, the impeller shell may be deformed to a large and undesirable extent. The state or manner of deformation may also change depending on the lot of the impeller. The fixing method utilizing caulking likewise can cause large amounts of unwanted deformation in the impeller shell.